Here are 6 tips to help keep sane, and survive anything from a 2 hour flight to a 15 or 16 hour flight, to make sure you're ready to begin your adventure soon after you arrive.
1. Wear loose fitting clothing.
If your destination doesn't require you wearing a suit as you exit the plane, then plan to wear comfy, loose fitting clothing that allows you to best relax. Keep tight clothing in your suitcase, which includes tight socks or shoes.
2. Stretch often.
Sitting in the same position for hours can not only cause your muscles to stiffen up and potentially pull, but can lead to blood clots. You should try to stand up every 2-3 hours, which could be as simple as walking to the bathroom and back. On top of this, you can stretch while in your seat, carefully rotating your head, stretching your arms above your head, and flexing your feet. When up in the aisle, without disrupting the flight crew, try to bend and stretch your legs and calves. Keep limber to avoid straining as you start your trip.
3. Drink lots of water.
Most people get dehydrated during longer flights because they don't feel like they need to drink water. The cabin pressure and just sitting for so long can make you feel bloated, and reduce the feeling that you need to drink more. Pushing past this and making yourself drink more water can help eleviate jet lag, and keep your body ready to start as soon as you are off the plane. I know this tip will be an issue for anyone with a window seat and a stranger between you and the aisle (and route to bathroom), but annoying someone a few times beats out the lack of energy and poor feeling you'll have after the flight. Along with this, try not to drink alcohol or anything with caffeine as this could leave you more dehydrated.
4. Plan to sleep.
Part of making yourself comfortable in tip 1 is to allow yourself to get some sleep. Most likely you got to the airport very early and now with a long flight ahead and time changes, you'll want to get at least a short nap. Beyond dressing properly, try to grab a blanket and pillow if offered by airline staff. Position the pillow behind your lower back for support and use the blanket to keep at a comfortable temperature. I've never been a fan of airline pillows for sleeping with, so packing an inflatable neck pillow could save you some sleep. Utilizing a sleep mask (or for backpackers, use a bandana), and ear plugs could give you a more restful sleep.
5. Bring enough activities to keep you occupied.
Just one book may not keep your attention for long enough, and you don't want the feeling of constantly looking at your watch and counting down the minutes. If you have an ebook reader like a Amazon Kindle
or iPad, fill it with a number of books or magazines. I've found shorter stories or articles work well for keeping your attention. Also with tablets, you can now watch movies, listen to music or play games, which can help during those long flights. Lastly, my wife and I liked playing games together during the flight, and a deck of cards can easily make for a good number of games.
6. Look for upgrades.
We all know that business class and first class have better seats than in coach, and sometimes the flight won't be completely full. If you're observant enough, and can ask nicely, sometimes a first class seat can become your new seat, giving more leg room, comfier cushions and a better flight overall. Alternatively, if you have a travel credit card or frequent flyer card, try to see if an upgrade can be bought with points.
Final notes. If you want to use something like sleeping pills, and you're traveling alone, be sure that all your valuables and passport are safe and tucked away.